In recent years, a light source for exposure needs to emit light at a short(er) wavelength as a semiconductor integrated circuit is designed more compact and circuit integration has a higher density. As a next-generation light source for exposing a semiconductor, developed is an extreme ultraviolet (hereinafter, occasionally referred to as “EUV”) light source device that emits extreme ultraviolet light at a wavelength of, particularly, 13.5 nm.
Several methods are known to cause the EUV light source device to emit EUV light. One of such methods heats and excites an extreme ultraviolet emission seed (EUV emission seed) to generate high temperature plasma, and extracts EUV light from the high temperature plasma.
An EUV light source device that employs such method is categorized into an LPP (Laser Produced Plasma) type and a DPP (Discharge Produced Plasma) type, depending upon a method used to generate high temperature plasma.
A DPP type EUV light source device applies a high voltage across a pair of electrodes, which is supplied with a discharge gas containing an extreme ultraviolet light emission seed, to generate high-density and high-temperature plasma upon electric discharging, and uses extreme ultraviolet light emitted therefrom. For use with the DPP type EUV light source device, a method has been proposed that includes supplying a surface of each electrode, which is used to generate electric discharge, with a raw material such as Sn (tin) or Li (lithium), and irradiating the raw material with an energy beam such as a laser beam for evaporation thereof such that high-temperature plasma is generated upon electric discharging. Such method is sometimes referred to as an LDP (Laser Assisted Discharge Produced Plasma) method or an LDP type. An LDP type EUV light source device is disclosed in, for example, Patent Literature Document 1. In Patent Literature Document 1 (Japanese Patent Application Laid-Open Publication No. 2007-505460), a pair of disk-shaped rotating electrodes are used as the above-mentioned electrodes, and the paired rotating electrodes are disposed such that the peripheral edges of the two rotating electrodes face each other.